Integumentary System Chapter 6 PDF

Functions of the Integumentary System Describe the general functions of the skin. Critical to maintaining homeostasis: Protection Sensation Thermoregulation Excretion Vitamin D Synthesis Protection - protecting underlying tissues from damage From mechanical trauma...

Functions of the Integumentary System Describe the general functions of the skin. Critical to maintaining homeostasis: Protection Sensation Thermoregulation Excretion Vitamin D Synthesis Protection - protecting underlying tissues from damage From mechanical trauma ○ Stratified squamous, keratinized epithelium protects body from mechanical trauma Provides a durable but flexible surface From pathogens ○ Provides a continuous barrier to invasion ○ Contains cells of immune system ○ Glands secrete a variety of antimicrobial substances Sebaceous gland secretions give surface of skin a slightly acidic pH (called acid mantle) From the environment ○ Skin absorbs ultraviolet (UV) radiation ○ Skin secretes lipid-based chemicals (hydrophobic) that have nonpolar covalent bonds ○ Critical for maintaining water and electrolyte homeostasis Sensation - Enables nervous system to perceive changes contacting the body Houses numerous sensory receptors ○ Detect potentially harmful stimuli such as heat & cold, pressure, sharpness, etc. Thermoregulation - The maintenance of a stable internal body temperature Determined by metabolism & muscle activity Uses negative feedback loops Excretion - Some waste products and toxins are eliminated from body through the skin Example: Lactic acid- from muscle metabolism Vitamin D Synthesis - Skin plays a critical role in vitamin D synthesis Precursor of Vit. D is a modified cholesterol found inside cells Skin Structure Largest organ, also known as cutaneous membrane 10-15% of total body weight Complex structure & performs many functions important for homeostasis 2 main components: ○ Epidermis ○ Dermis Epidermis is avascular O₂ & nutrient diffusion from blood vessels in dermis ○ Limits epidermal thickness Superficial layers = dead cells Dermis and other components Accessory structures of skin – embedded in cutaneous membrane: ○ Sweat glands, sebaceous glands, hair, and nails Sensory receptors Arrector pili muscles Hypodermis Superficial fascia or subcutaneous tissue Deep to dermis, not part of skin Anchor skin to deeper structures ○ Muscle and bone Loose CT + adipose tissues + abundant blood supply ○ Good place to administer SQ injections Functions: ○ Keep the body's temperature stable ○ Energy storage ○ Protection ○ Acts as a passageway for the nerves and blood vessels from the dermis to the muscles The Epidermis - primary function is protection Primary function is protection Composed of several cell types Most numerous are keratinocytes (95%) ○ Kerato- = “horn” Keratinocytes: have 2 structural features that make epidermis stronger: ○ Manufacture keratin – tough fibrous protein ○ Linked by desmosomes Layers of the Epidermis Keratinocytes are arranged into layers or strata: (Superficial to deep/ not all have 5 layers) ○ Stratum corneum  ○ Stratum lucidum ○ Stratum granulosum ○ Stratum spinosum ○ Stratum basale Stratum basale – (stratum germinativum) ○ Single layer of stem cells resting on basement membrane ○ Nearest to blood supply ○ Most metabolically and mitotically active cells ○ Involved in Vit. D synthesis & replacement of dead keratinocytes Stratum spinosum ○ Thickest layer ○ spino- = “prickly” ○ Sits on top of stratum basale ○ Near blood supply ○ Metabolically and mitotically active ○ Help produce Vit. D. Stratum granulosum ○ 3 to 5 layers of cells ○ Prominent cytoplasmic granules Filled with keratin bundles and a lipid-based substance Both secreted by exocytosis Lipid-based substances coats this strata + superficial layers Isolates the cells from water and nutrients Stratum lucidum – narrow layer of clear, dead keratinocytes ○ Found only in thick skin Stratum corneum Outermost layer of epidermis Several layers of dead flattened keratinocytes ○ Lost organelles and filled mostly with keratin bundles with thickened plasma membranes ○ Loss of desmosomes - sloughed off or exfoliated mechanically Keratinocyte Life Cycle Continuous loss of dead cells - Stratum basale and spinosum must divide via mitosis (primarily at night): ○ As deeper strata divide they push cells above them into more superficial layers Migration from deepest strata to stratum corneum takes a cell between 4050 days to complete Other Cells of the Epidermis Dendritic (Langerhans) cells ○ Located in stratum spinosum ○ Phagocytes of immune system Melanocytes ○ Located in stratum basale ○ Produce melanin (skin pigment ranging from orange-red to brown-black) Merkel cells – oval cells ○ Located scattered throughout stratum basale Sensory receptors associated with small neurons in dermis Detect light touch and discriminate shapes and textures ○ Found in large numbers in regions that are specialized for touch Fingertips, lips, and at base of hairs Thick Skin Palms of hand and sole of foot Subject to great degree of mechanical stress Contain all 5 epidermal strata ○ Include very thick stratum corneum Lack hair follicles Numerous sweat glands Palms of hand and sole of foot Subject to great degree of mechanical stress Contain all 5 epidermal strata Include very thick stratum corneum Lack hair follicles Numerous sweat glands Rest of the body Subject to less mechanical stress ○ Contains only 4 layers Stratum lucidum is missing Each layers is thinner than thick skin layers Numerous hairs, sweat glands, and sebaceous glands Callus – additional layers of stratum corneum ○ Form in either thick or thin skin due to repetitive pressure The Dermis Highly vascular layer deep to epidermis Functions:  ○ Provides blood supply for epidermis ○ Contains sensory receptors ○ Anchors epidermis in place Composed of 2 distinct layers of connective tissue ○ Papillary layer ○ Reticular layer The Papillary Layer Thinner most superficial layer (accounts for 20% of depth) Composed of loose connective tissue: ○ Ground substance > collagen and elastic fibers Special collagen fibers extends into epidermal basement membrane to anchor epidermis to dermis Repetitive trauma blister ○ Fibroblasts & phagocytes Dermal papillae: folded projections ○ House capillaries ○ House tactile (meissner) corpuscles Sensory receptors that respond to light touch Numerous in fingertips, lips, face, & external genitalia The Reticular Layer Deeper and thicker layer Separates dermis from hypodermis Composed of mostly dense irregular connective tissue: ○ Many irregularly arranged collagen bundles Collagen bundles strengthen dermis and prevent traumatic injuries ○ Elastic fibers allow dermis to return to its original shape & size after stretching Extreme stretching striae or stretch marks Skin Markings Small visible lines in epidermis created by interaction between dermis and epidermis ○ Most obvious are seen on thick skin Reticular layer is also responsible for skin markings: ○ In areas of body that see a lot of movement, such as surrounding joints, reticular layer is tightly anchored to deeper structures that create deep creases called flexure lines Melanin Skin color – mostly depends on the type and concentration of the pigment melanin. Derived from amino acid tyrosine Brownish black and reddish varieties People produce different types and quantities, imparting pigment to skin Melanin produced by melanocytes and transferred to stratum basale and spinosum (in epidermis)  Melanosomes (melanin-containing organelles) migrate to ends of extensions - released by exocytosis - keratinocytes take up melanin via endocytose - melanin transported to superficial side of nucleus - shields DNA from UV radiation ○ Melanin degrades after a few days ○ Must be made continuously to maintain a consistent skin color Primary function: Protecting keratinocyte DNA from mutations induced by UV radiation – Evolutionarily Advantageous? More UV radiation - more melanin synthesized tanning or darkening of skin pigmentation Secondary function: ○ Reduce synthesis of vitamin D in response to UV radiation Maintain Vitamin D within a narrow range prevent calcium imbalance Acclimation by an individual to high UV-conditions (e.g., tanning) Evolution of darker/lighter skin tones in humans lineages living in high- or low- UV exposure regions (e.g., closer or further from equator) Skin Color as a Diagnostic Tool Color changes associated with amount of blood flow in dermis can be useful in diagnosis of disease: Erythema –blood flow in dermis increases skin more reddish (red color due to hemoglobin, red pigments in red blood cells) ○ Normal response to exercise where blood flow in dermis has increased to maximize heat released to external environment ○ Other conditions: trauma, fever, infection and cyanide poisoning Pallor – occurs when blood flow in dermis decreases loss of normal pinkish hue whitish color of collagen in dermis ○ Normal response when body is trying to conserve heat in a cold environment Cyanosis – sign that someone needs immediate attention ○ Hemoglobin has very low levels of bound oxygen blood turns reddish purple skin has a faint bluish hue ○ Occur when: Someone has difficulty breathing Hemoglobin or red cell levels are low in blood Hemoglobin is unable to bind to oxygen Accessory Structures or Appendages Accessory structures or appendages: hair, nails, & glands ○ Derived from epithelium only ○ Assists in performing overall function Hair (pili) – small filamentous structures that protrude from surface of skin ○ Over entire body except: Regions with thick skin, lips, and parts of external genitalia Role of hair –  ○ Thermoregulation? Too sparse in humans to play a significant role, as it does in other mammals ○ Protection: By preventing substances and organisms of external environment from entering eyes and nose On head, protects underlying skin of scalp from UV radiation and mechanical trauma ○ Plays a role in detecting changes in environment Each strand of hair is associated with a small sensory neuron Hair Structure Composed of 2 main parts: ○ Shaft ○ Root Both made up of stratified squamous keratinized epithelial cells in various stages of development Shaft Part of hair that projects from skin’s surface Dead keratinized epithelial cells that have completed keratinization process Strand of hair has 3 visible regions in a transverse section: Root Segment of hair embedded in dermis Surrounded by a small sensory neuron Living epithelial cells undergoing keratinization Hair papilla: Root is indented at its base by a projection of blood vessels from dermis Matrix – small number of keratinocytes found at base of root ○ Actively divide via mitosis Root is embedded in hair follicle Hair follicle = in-folding of epidermis called epithelial root sheath Extends deep into dermis or even hypodermis Dermal root sheath: surrounding epithelial root ○ Consists of connective tissue ○ Supports follicle and keeps it separate from dermis Arrector Pili Muscles Small bands of smooth muscle Attached to dermal root sheath & dermal papillary layer Piloerection: Contraction of these tiny muscles causes hair to stand up ○ Gives skin a dimpled appearance, commonly called “goosebumps” One of the body’s response to decreased environmental temperature ○ Trap a layer of warm air closer to the skin surface to help maintain body temperature Hair Growth Hair growth averages 11.5 cm per month but varies between individuals Growth is not continuous but occurs in a cycle with 2 main phases: ○ Growth stage ○ Resting stage Hair Growth Stage Mitosis occurs in matrix: Cells divide and push cells above - farther away from blood supply - keratinize and die Stage varies in duration from a month to as long as six years ○ Eyelashes = 1 month (Growth Stage) ○ Scalp = 6 years (Growth Stage) Resting stage: mitosis in matrix ends as cells die: ○ Follicle shortens - hair is pushed toward surface where it remains dormant for a month to several months ○ Falls out on its own or is pushed out by a new hair in growth stage Hair Resting Stage Mitosis in matrix ends as cells die: Follicle shortens - hair is pushed toward surface where it remains dormant for a month to several months Falls out on its own or is pushed out by a new hair in growth stage Nails (different keratin) Hard accessory structures composed of stratified squamous epithelium filled with hard keratin Nail plate – most visible component of nail, sits on top of an underlying epidermal nail bed ○ Divided into: Nail body – visible portion of nail plate Nail root – portion of plate that lies under skin Where nail matrix containing actively dividing cells is found Folded regions of skin surround and reinforce nail plate: ○ Proximal nail fold – on proximal edge covering nail root ○ Eponychium /eponi kyum/ (cuticle): distal edge of nail fold Consists of only stratum corneum ○ Medial and lateral nail folds – on medial and lateral edges of nail plate respectively ○ Hyponychium – underlying free edge of nail plate Nail Growth Occurs at nail matrix - actively dividing cells push neighboring keratinocytes distally - die once keratinization is completed and have been cut off from blood supply Fingernails grow an average of 0.5 mm per week Toenails grow more slowly Nails do not contain melanocytes ○ Mostly translucent except at region called lunula /lah new lah/  ○ Lunula: half-moon shaped region of proximal nail plate that represents an accumulation of keratin ○ Indicator of good health – if more distinctive Primary function of nails – ○ Protection of underlying tissue (distal tips of the fingers and toes) from trauma ○ Can be used as tools, enabling more precise gripping of items when picked up Glands Skin contains 2 basic types of glands ○ Sweat glands: produce sweat ○ Sebaceous glands: produce oily sebum Both derived from epithelial cells in epidermis but located deeper in dermis Sweat Glands 4 types of sweat glands that differ structurally and in products secreted ○ Eccrine sweat glands ○ Apocrine sweat glands ○ Ceruminous glands Secrete cerumen (earwax) ○ Mammary glands Secrete milk Eccrine Sweat Glands Simple coiled tubular glands found in dermis - exit through duct sweat pores - epidermal surface Contains: 99% water, waste products (lactic acid), electrolytes (Na+, K+, Cl- ions), antimicrobial compounds, and has slightly acidic pH Function: excretion, protection & thermoregulation (primary) Aporcrine Sweat Glands Found in axillae, anal area, and areola Large glands that release a protein-rich secretion into a hair follicle Secretions can become odoriferous once skin bacteria metabolize their contents Influenced by sex hormones Become active after puberty Sebaceous Glands Branched glands with clusters of secretory cells (acini) surrounded by small ducts ○ Converge to form a central duct that empties into hair follicle or small pore ○ Produce sebum (waxy, oily mixture of mostly lipids) Function: inhibits water loss, inhibits bacterial growth Found everywhere on body except palms and soles (greatest number found on face and scalp) Secretion is influenced by sex hormones (especially male sex hormone testosterone)  Dramatic increase in sebum production occurs after puberty